Barbaro was expected to undergo surgery early Sunday afternoon to repair multiple fractures in his right hind leg in a bid to save his life, ESPN's Jeannine Edwards reported.
The surgery to repair the injuries, suffered in the first furlong of the Preakness Stakes on Saturday, was exected to take two hours. Doctors expected to learn through the surgery whether the bay colt had also sustained vascular and soft tissue damage that would make a recovery more difficult, if not impossible, Edwards reported.
It was all a dramatic turn from Saturday, when Barbaro seemed poised to take the next step in becoming the first Triple Crown winner since Affirmed in 1978. Instead, Bernardini won the $1 million Preakness, beating Sweetnorthernsaint by 5¼ lengths.
At the starting gate, Barbaro was eager to go. The unbeaten Kentucky Derby winner gave jockey Edgar Prado every indication he was set for the race of his life.
The strapping bay colt was bucking in the starting gate at Pimlico Race Course, and he even broke through early. All seemed well after Prado reined him in and returned to the No. 6 gate for a second start.
About 12 seconds later, the question wasn't whether Barbaro would win the Triple Crown, but whether he would live.
After galloping a few hundred yards in the Preakness, Barbaro's right rear leg flared out and he veered sideways while eight rivals passed him.
The record crowd of 118,402 watched in shock as Prado pulled the powerful horse to a stop and jumped off. With Barbaro still on the track and running on three legs, there wasn't much enthusiasm for the finish, especially with many of the fans in tears.
Barbaro, thought by many to be a serious contender for the Triple Crown, was diagnosed with a fracture above and below his ankle. Dr. Larry Bramlage, of the American Association of Equine Practitioners, called it a "life-threatening" injury.
The horrifying scene occurred directly in front of the grandstand as the field of nine headed to the first turn. The 1-2 favorite -- with six straight victories -- was in the middle of the pack when he suddenly dropped back.
"During the race, he just took a bad step," Prado said. "I heard a noise about 100 yards into the race and pulled him right up."
The colt was noticeably favoring his right rear leg.
"It's a serious fracture. This will require pretty major surgery," Bramlage said. "Keep your fingers crossed and say a prayer. His career is over. This is very life-threatening.
"Under the best circumstances, we will try to save him as a stallion."
Bramlage said a human would have to spend six weeks in bed with a comparable fracture, and "with a horse that's impossible."
Barbaro was taken back to his barn, where he was X-rayed, tranquilized and stabilized before being transported to the University of Pennsylvania's New Bolton Center, a veterinary facility, in Kennett Square.
Trainer Michael Matz said surgery would be performed Sunday.
"We just have to pray for the best," he said.
Bramlage said Barbaro breaking through the gate before the official start had nothing to do with the injury.
As soon as his horse broke down, Matz bolted from his seat and ran onto the track.
Also on the track was owner Gretchen Jackson, and Prado told her, "I'm sorry, I'm sorry."
She put an arm on his shoulder and said, "You did a great job."
Fans were crying in the grandstand as Barbaro was loaded into an equine ambulance and taken away, his injured leg in an inflatable cast.
"You never expect it," Jackson said.
The devastating development drained all the excitement from a Pimlico crowd expecting a victory by Barbaro that would have set the stage for seventh Triple Crown try in the last 10 years.
The Triple talk is over now.
Bernardini took control from pacesetter Like Now and pulled away for his victory after an impressive move around the far turn.
Hemingway's Key was third behind Sweetnorthernsaint, followed by Brother Derek, Greeley's Legacy, Platinum Couple, Like Now and Diabolical.
Ridden by Javier Castellano, Bernardini became the first Preakness winner who didn't run in the Derby since Red Bullet in 2000.
"It's very exciting for everyone, for me especially, to win the Preakness. It's also very, very sad. It's a big disappointment," Castellano said.
Lightly raced, Bernardini was taking a major step up in class in just his fourth career start. The well-bred son of A.P. Indy came into $1 million Preakness off an impressive win in the Withers Stakes at Aqueduct on April 29.
The colt has now won three straight after running fourth in his debut, and earned $650,000 for Darley Stable, operated by Dubai's Sheik Mohammed.
Winning time for the 1 3/16 miles was 1:54.65, off the stakes record of 1:53.40.
Bernardini paid $27.80, $9.40 and $5.80. Sweetnorthernsaint, who finished seventh in the Derby, returned $7.80 and $5. Hemingway's Key paid $8.
Winning trainer Tom Albertrani said he didn't see Barbaro break down.
"I saw Michael run by me and I knew something was wrong," Albertrani said. "You feel very upset when you see something like that."
D.D. Matz, the trainer's wife, said Barbaro was behaving "like the true champion that he is and, hopefully, he'll get the best care possible and be all right."
Barbaro's injury came a year after Afleet Alex's brush with catastrophe. Turning for home, the horse was bumped by another and nearly knocked to his knees before gathering himself and going on to win.
Thoroughbreds have broken down in the past in big races: In the 1993 Preakness, Union City broke down and was euthanized; in the 1993 Belmont Stakes, Preakness winner Prairie Bayou broke down; in the 1999 Belmont Stakes, with Charismatic trying to win the Triple Crown, he was pulled up while finishing third with a fractured ankle; Go For Wand broke down in the stretch of the 1990 Breeders' Cup Distaff and was euthanized; and in 1975, Ruffian broke down in a match race with Foolish Pleasure. She was operated on but later was euthanized.
The Associated Press contributed to this report.